Archive for the ‘ Lunix ’ Category

Top 25 Best Linux Commands

Top 25 Best Linux Commands.

25) sshfs name@server:/path/to/folder /path/to/mount/point
Mount folder/filesystem through SSH
Install SSHFS from http://fuse.sourceforge.net/sshfs.html
Will allow you to mount a folder security over a network.

24) !!:gs/foo/bar
Runs previous command replacing foo by bar every time that foo appears
Very useful for rerunning a long command changing some arguments globally.
As opposed to ^foo^bar, which only replaces the first occurrence of foo, this one changes every occurrence.

23) mount | column -t
currently mounted filesystems in nice layout
Particularly useful if you’re mounting different drives, using the following command will allow you to see all the filesystems currently mounted on your computer and their respective specs with the added benefit of nice formatting.

22) <space>command
Execute a command without saving it in the history
Prepending one or more spaces to your command won’t be saved in history.
Useful for pr0n or passwords on the commandline.

21) ssh user@host cat /path/to/remotefile | diff /path/to/localfile –
Compare a remote file with a local file
Useful for checking if there are differences between local and remote files.

20) mount -t tmpfs tmpfs /mnt -o size=1024m
Mount a temporary ram partition
Makes a partition in ram which is useful if you need a temporary working space as read/write access is fast.
Be aware that anything saved in this partition will be gone after your computer is turned off.

19) dig +short txt <keyword>.wp.dg.cx
Query Wikipedia via console over DNS
Query Wikipedia by issuing a DNS query for a TXT record. The TXT record will also include a short URL to the complete corresponding Wikipedia entry.

18) netstat -tlnp
Lists all listening ports together with the PID of the associated process
The PID will only be printed if you’re holding a root equivalent ID.

17) dd if=/dev/dsp | ssh -c arcfour -C username@host dd of=/dev/dsp
output your microphone to a remote computer’s speaker
This will output the sound from your microphone port to the ssh target computer’s speaker port. The sound quality is very bad, so you will hear a lot of hissing.

16) echo “ls -l” | at midnight
Execute a command at a given time
This is an alternative to cron which allows a one-off task to be scheduled for a certain time.

15) curl -u user:pass -d status=”Tweeting from the shell” http://twitter.com/statuses/update.xml
Update twitter via curl

14) ssh -N -L2001:localhost:80 somemachine
start a tunnel from some machine’s port 80 to your local post 2001
now you can acces the website by going to http://localhost:2001/

13) reset
Salvage a borked terminal
If you bork your terminal by sending binary data to STDOUT or similar, you can get your terminal back using this command rather than killing and restarting the session. Note that you often won’t be able to see the characters as you type them.

12) ffmpeg -f x11grab -s wxga -r 25 -i :0.0 -sameq /tmp/out.mpg
Capture video of a linux desktop

11) > file.txt
Empty a file
For when you want to flush all content from a file without removing it (hat-tip to Marc Kilgus).

10) $ssh-copy-id user@host
Copy ssh keys to user@host to enable password-less ssh logins.
To generate the keys use the command ssh-keygen

9) ctrl-x e
Rapidly invoke an editor to write a long, complex, or tricky command
Next time you are using your shell, try typing ctrl-x e (that is holding control key press x and then e). The shell will take what you’ve written on the command line thus far and paste it into the editor specified by $EDITOR. Then you can edit at leisure using all the powerful macros and commands of vi, emacs, nano, or whatever.

8 ) !whatever:p
Check command history, but avoid running it
!whatever will search your command history and execute the first command that matches ‘whatever’. If you don’t feel safe doing this put :p on the end to print without executing. Recommended when running as superuser.

7) mtr google.com
mtr, better than traceroute and ping combined
mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
As mtr starts, it investigates the network connection between the host mtr runs on and HOSTNAME. by sending packets with purposly low TTLs. It continues to send packets with low TTL, noting the response time of the intervening routers. This allows mtr to print the response percentage and response times of the internet route to HOSTNAME. A sudden increase in packetloss or response time is often an indication of a bad (or simply over‐loaded) link.

6 ) cp filename{,.bak}
quickly backup or copy a file with bash

5) ^foo^bar
Runs previous command but replacing
Really useful for when you have a typo in a previous command. Also, arguments default to empty so if you accidentally run:
echo “no typozs”
you can correct it with
^z

4) cd –
change to the previous working directory

3):w !sudo tee %
Save a file you edited in vim without the needed permissions
I often forget to sudo before editing a file I don’t have write permissions on. When you come to save that file and get the infamous “E212: Can’t open file for writing”, just issue that vim command in order to save the file without the need to save it to a temp file and then copy it back again.

2) python -m SimpleHTTPServer
Serve current directory tree at http://$HOSTNAME:8000/

1) sudo !!
Run the last command as root
Useful when you forget to use sudo for a command. “!!” grabs the last run command.

Vim vi how to reload a file your editing

Maiar’s Vault: Vim vi how to reload a file your editing.

5.8. How do I reload current file?

You can use the “:edit” command, without specifying a file name, to reload
the current file. If you have made modifications to the file, you can use
“:edit!” to force the reload of the current file (you will lose your modifications).

For more information, read: http://vimdoc.sourceforge.net/cgi-bin/vimfaq2html3.pl#5.8

:help :edit
:help :edit!
:help 'confirm'

How to change default I/O scheduler

How to change default I/O scheduler? | Planet Admon.

Red Hat Enterprise Linux 3 with a 2.4 kernel base uses a single, robust, general purpose I/O elevator. The I/O schedulers provided in Red Hat Enterprise Linux 4, embedded in the 2.6 kernel, have advanced the I/O capabilities of Linux significantly. With Red Hat Enterprise Linux 4, applications can now optimize the kernel I/O at boot time, by selecting one of four different I/O schedulers to accommodate different I/O usage patterns:

* Completely Fair Queuing—elevator=cfq (default)
* Deadline—elevator=deadline
* NOOP—elevator=noop
* Anticipatory—elevator=as

The I/O scheduler can be selected at boot time using the “elevator” kernel parameter. In the following example, the system has been configured to use the deadline scheduler in the grub.conf file.

title Red Hat Enterprise Linux Server (2.6.18-8.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-8.el5 ro root=/dev/vg0/lv0 elevator=deadline
initrd /initrd-2.6.18-8.el5.img

In Red Hat Enterprise Linux 5, it is also possible to change the I/O scheduler for a particular disk on the fly.

# cat /sys/block/sdb/queue/scheduler
noop anticipatory deadline [cfq]
# echo ‘deadline’ > /sys/block/sdb/queue/scheduler
# cat /sys/block/sdb/queue/scheduler
noop anticipatory [deadline] cfq

The following are the tunable files for the deadline scheduler. They can be tuned to any suitable value according to hardware performance and software requirements:

/sys/block/DEVNAME/queue/iosched/read_expire
/sys/block/DEVNAME/queue/iosched/write_expire
/sys/block/DEVNAME/queue/iosched/fifo_batch
/sys/block/DEVNAME/queue/iosched/write_starved
/sys/block/DEVNAME/queue/iosched/front_merges

DEVNAME is the name of block device (such as sda, sdb, hda, etc)

A detailed description of the deadline I/O scheduler can be found at:
/usr/share/doc/kernel-[version]/Documentation/block/deadline-iosched.txt.

http://www.redhat.com/magazine/008jun05/features/schedulers/

http://www.redbooks.ibm.com/abstracts/redp4285.html

Random read performance per I/O elevator (synchronous)

Random read performance per I/O elevator (synchronous)

CPU utilization by I/O elevator (asynchronous)

CPU utilization by I/O elevator (asynchronous)

 Impact of nr_requests on the Deadline elevator (random write ReiserFS)

Impact of nr_requests on the Deadline elevator (random write ReiserFS)

Impact of nr_requests on the CFQ elevator (random write Ext3)

Impact of nr_requests on the CFQ elevator (random write Ext3)

Random write throughput comparison between Ext and ReiserFS (synchronous)

Random write throughput comparison between Ext and ReiserFS (synchronous)

 Random write throughput comparison between Ext3 and ReiserFS (asynchronous)

Random write throughput comparison between Ext3 and ReiserFS (asynchronous)